Adjustable condenser microphone



Sept. 16, 1958 K. SCHOEPS, ETAL 2,852,620

ADJUSTABLE CONDENSER MICROPHONE Filed Aug. 9, 1955 20 Z s m 4/s- I7 r ll l l 1' I l I I H Ill/[m [z a I ,6 I3 I 7 /.5' /l III ,9 ,3 a be M [:IZZNTORS Wad v a microphone having unidirectional characteristics.

United Sttes Patent F ADJUSTABLE CONDENSER MICROPHONE Karl Schoeps and Willy Kiisters, Karlsruhe-Durlach, Germany Application August 9, 1955, Serial No. 527,347

Claims priority, application Germany August 13, 1954 6 Claims. (Cl. 179-106) The present invention relates to an adjustable condenser microphone. More particularly, the present invention relates to an adjustable condenser microphone adapted to operate in either a unidirectional or polydirectional manner.

In the microphone art today, it is possible to construct That is, the microphone will respond to sound wavestransmitted through the surrounding atmosphere coming only from a particular direction. This is usually done by providing a separate sound path to the inner surface of the vibrating diaphragm used in the microphone. A delay line member can be provided in this path. This delay line member introduces a specific time delay in the transmission of sound waves therethrough.

Accordingly, the unidirectional characteristics are imparted to the microphone by arranging the dimensions of the microphone so that the time delay introduced by the delay line member is equal to the time taken by the sound waves impinging on the outer surface of the diaphragm to reach the air chamber. Therefore, the micro- .phone will be responsive to sound waves coming only from the direction corresponding to the outer surface of the microphone. The sound waves coming from the other directions will be delayed by the predetermined time delay and when they reach the air chamber of the microphone, they will be cancelled by the waves already transmitted to the air chamber by means of the vibrating diaphragm.

Therefore, the sound waves coming from all directions except from directly in front of the outer surface of the diaphragm will have no effect on the vibration of the diaphragm.

Accordingly, it is common today to choose a microphone having either unidirectional or polydirectional characteristics. If a microphone is used before an audience, for example, and the sounds from the audience are undesired, the unidirectional microphone is used so that sound waves coming only from one side of the microphone will affect the microphone diaphragm.

On the other hand, if it is desired to have the micro- 7 phone respond to sound waves emanating from a plurality "of directions at one time, it is common to use a microphone having a spherical characteristic which, for the purpose of this application, will be considered to be a polydirectional microphone. Such microphones are used, for example, with large choral groups and orchestras as well as for many other similar purposes.

The condenser microphone is a particularly advantageous type of microphone in that it may be made quite small and still faithfully reproduce the sound waves impinging thereon. The condenser microphone is usually a pressure-operated type so that it has substantially polydirectional characteristics. Condenser microphones constructed in accordance with the present invention may be used to exhibit either unidirectional or polydirectional characteristics as desired. 7

It is accordingly an object of the present invention to provide a new and improved condenser microphone.

2,352,625 Patented Sept. 16, 1958 "ice A second object of the present invention is to provide a new and improved condenser microphone which may be adjusted to exhibit either unidirectional or polydirectional characteristics.

Another object of the present invention is to provide a new and improved condenser microphone which'may be remotely adjusted so that it operates in either a unidirectional or polydirectional manner.

With the above objects in view, the present invention relates to an adjustable condenser microphone adapted to operate in either a unidirectional. or polydirectional manner and including an open-ended casing, a diaphragm mounted at one er& of the casing to hermetically seal the same from the surrounding atmosphere, the diaphragm having an inner anclouter surface and adapted to be vibrated by sound Waves transmitted through the surrounding atmosphere and impinging on the outer surface thereof, a rear electrode fixedly mounted in the casing and spaced from the inner surface of the diaphragm, wall means forming a vibration chamber in the casing the volume of which is varied during vibration of the diaphragm, air passage means in the casing for providing a path for the flow of air between the vibration chamber and the surrounding atmosphere, and valve means associated with the casing and movable between an air passage opening position wherein the air from the atmosphere reaches the vibration chamber through the air passage means causing the microphone to operate 'ina unidirectional manner, and an air passage closing position wherein the air from the surrounding atmosphere is prevented from reaching the vibrating chamber and the microphone operates in a polydirectional manner.

- The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to itsconstruction and itsmethod of operation, to gether with additional objects and advantages thereof, will be best understood from the following description of within an open-ended tubular casing 3, one end of which is hermetically sealed by means of a diaphragm 1. The diaphragm 1 is mounted on the endof the casing 3 in a pretensioned manner by means of an annular ring 2 which may be fastened to the casing 3 in conventional manner.

Opposite the inner surface of the diaphragm 1 is mounted the upper planar surface of the rear electrode 4 which has a coaxial portion extending through the bottom plate 16 of the microphone casing. The planar portion of the rear electrode 4 contains a plurality of axially directed channels 9. These channels 9 provide friction damping of the vibrating system of the microphone.

The rear electrode 4 is insulated from the casing by means of an annular electrically insulated ring 6. The effective air or vibration chamber of the condenser microphone is bounded by the inner surface ofthe membrane 1 at one end and by a disc 7 which is mounted on the rear electrode 4 at the other end. The air or vibration chamber includes the air in the channels 9 of the rear electrode. The disc 7 is positioned by means of a thread- .ed .collet 8 which is mounted on the rear electrode 4.

Contained in the disc 7 is a plurality of axially directed channels 10 which are aligned with a corresponding plurality of radially directed air passages or grooves 11 located in the top surface of thecollet 8. Opposite the radial passages 11 and in the wall of the easing 3 is located aplurality of radially directed channels 12L This permits the surrounding atmosphere 'to' enter into the interior of the casing 3 through the channels 12 and into the air or vibration chamber of the microphone through the air passages 11 and channels 10.

.Located beneath the disc 7 and slidably I ounted on the collet 8 is an annular valve member 13 hich may be axially moved to totally or partially block the inner end of the channals 12 in the wall of the casing 3. The

valve member 13 may be axially moved by a rod 14 extending through a passage 15 in the wall of the casing 3. In the position shown, the valve member 13 is inits maximum downwardly directed position so that air from the surrounding atmosphere is free to enter into the interior of the microphone vibration chamber.

It is apparent that the valve member 13 may also be rotatably mounted and the channel 15 may have a spiral form so that the valve member 13 may be held in any particular position between fully opened and fully closed by means of manually moving the rod 14 about the axis of the casing 3. This is similar to a bayonet" type of mounting. It is also possible to remotely operate the valve member 13. For this purpose a coil spring 19 is provided between the bottom surface of the valve member 13 and the bottom portion 16 of the casing 3. This spring tends to normally urge the valve member 13 into fully closed position. A solenoid coil 17 is also mounted beneath the valve member 13 and cooperates with an armature 18 mounted in the valve member 13 and made of an electromagnetic material. It is apparent that when the solenoid coil 17 is energized, the armature 18 will be attracted thereto and will be moved downwardly, thereby moving the valve member 13 into its open position against the action of the coil spring 19. The size of the parts of the condenser microphone illustrated in Fig. 1 are chosen to correspond to the size required for a polydirectional condenser microphone. Similarly, the distance between the inner surface of the diphragm 1 and the upper planar surface of the rear electrode 4 is set at the proper distance for an ordinary polydirectional condenser microphone. The stiffness, mass and friction elements are chosen in the same manner as for a polydirectional microphone. Accordingly, when the coil spring 19 has moved the valve member 13 into its fully closed position to keep out the air from surrounding atmosphere by blocking the channels 12, all the sound waves impinging on the diaphragm 1 will be effective in producing vibrations of the diaphragm. The condenser microphone will then operate as a conventional, poly directional condenser microphone wherein the variation of distance between the diaphragm 1 and the rear electrode 4 will change the capacity between these two members and eifect a proportional change in the electrical potential between these two members. It is clear that the diaphragm 1 and the rear electrode 4 are both made of electrically conductive materials which are electrically insulated from each other by means of the annular ring 6.

It is apparent that in accordance with the conventional condenser microphone, a predetermined electrical potential is applied between the two parts of the condenser, namely the diaphragm 1 and the rear electrode 4. The channels-9 in the rear electrode 4 will provide the proper friction damping for the vibrations set up in the vibration chamber which includes the air between the diaphragm 1' and the rear electrode 4, the air in the channels 9 of the rear electrode and the air between the rear electrode 4 and the disc 7. In addition, a small amount of air is maintained in the channels-1t) of the discs 7 and the grooves 11 of the coil 8 when the valvemember 13 is in the fully closed position.

, If the valve member is manually or electromagnetically moved to the open illustrated position, thevibrating chamber will be open to the surrounding atmosphere by frictional resistance to the air fiow therethrough so that a predetermined time is taken for the air introduced through the channels 12 to reach the vibration chamber of the microphone above the disc 7. The time required for the air from the surrounding atmosphere to be introduced into the vibration chamber of the microphone represents a time delay. In accordance with the principles of the present invention this time delay corresponds to the time taken by the sound waves introduced into the vibration chamber by the vibration of the diaphragm 1 to reach the portion of the vibration chamber above the disc 7.

Accordingly, the sound waves impinging on the outer surface diaphragm will set up proportional vibrations in the diaphargm, which vibrations will be transmitted through the channels 9 of-the rear electrode into the bottom portion of the air chamber located between the rear electrode 4 and the disc 7. These vibrations, produced by the sound waves impinging on the outer surface of the diaphragm, will reach this portion of the vibration chamber at the same time, and the proper phase has sound waves which have been introduced into the microphone casing through the channels 12 and which have passed through the delay means made up of the grooves 11 and channels 10. Accordingly, these sound waves will cancel each other in the vibration chamber and those sound waves which have been introduced through the channels 12 will be cancelled in the vibration chamber and have no effect on the vibration of the diaphragm 1. That is, no pressure gradient across the diaphragm 1 is produced by the sound waves reaching the vibration chamber through the channels 12.

Therefore, only the sound waves arriving at the microphone which impinge directly upon the outer surface of the diaphragm 1 will be effective in producing vibration of-the diaphragm 1 with the corresponding change in the capacitance between diaphragm 1 and the rear electrode 4. Accordingly, a unidirectional microphone is now provided.

From the above description it is apparent that the condenser microphone constructed in accordance with the present invention may be adjusted to operate as a unidirectional microphone or as a polydirectional microphone. When the valve member 13 is in the illustrated air passage opening position, the microphone will operate as a unidirectional microphone since the sound waves from the surrounding atmosphere can enter the interior of the microphone through the channels 12. On the other hand, when the valve member 13 is in the unillustrated air passage closed position, the condenser microphone Will operate as a polydirectional microphone since sound waves emanating in the surrounding atmosphere can only afiect the vibration by vibrating the diaphragm 1.

All of the channels 9, 1t) and 12 and the grooves 11 are preferably of constant diameter so that the flow of air can be effected in the desired manner.

An additional feature of the present invention is the use of the annular member 20 mounted on the front end of the microphone. The member 20 provides a sound detour path for the sound waves to insure that the proper relation of the phases exists between the sound waves passing through the air delay means and by other sound waves reaching the microphone.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of adjustable microphones diifering from the types described above.

While the invention has been illustrated and described as embodied in an adjustable condenser microphone adapted to operate in either a unidirectional or polydirectional manner, it is not intended to be limited to the details shown, since various modifications and structural changes may be 'made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. An adjustable condenser microphone adapted to operate in either a unidirectional or polydirectional manner, comprising, in combination, an open-ended casing; a diaphragm mounted at one end of said casing to hermetically seal the same from the surrounding atmosphere, said diaphragm having an inner and outer surface and adapted to be vibrated by sound waves transmitted through said surrounding atmosphere and impinging on said outer surface thereof; a rear electrode fixedly mounted in said casing and spaced from said inner surface of said diaphragm; wall means forming a vibration chamber in said casing, the volume of which is varied during vibration of said diaphragm; air passage means in said casing for providing a path for the flow of air between said vibration chamber and said surrounding atmosphere; and valve means associated with said casing and movable between an air passageopening position, wherein the air from said atmosphere reaches said vibration chamber through said air passage means causing said microphone to operate in a unidirectional manner, and an air passage closing position wherein the air from said surrounding atmosphere is prevented from reaching said vibrating chamber and said microphone operates in a polydirectional manner.

2. An adjustable condenser microphone adapted to 0p erate in either a unidirectional or polydirectional manner, comprising, in combination, an open-ended casing; a diaphragm mounted at one end of said casing to hermetically seal the same from the surrounding atmosphere, said diaphragm having an inner and outer surface and adapted to be vibrated by sound waves transmitted through said surrounding atmosphere and impinging on said outer surface thereof; a rear electrode fixedly mounted in said casing and spaced from said inner surface of said diaphragm; wall means forming a vibration chamber in said casing the volume of which is varied during vibration of said diaphragm; air passage means in said casing for providing a path for the flow of air between said vibration chamber and said surrounding atmosphere; and electromagnetically operated valve means associated with said casing and movable between an air passage opening position, wherein the air from said atmosphere reaches said vibration chamber through said air passage means causing said microphone to operate in a unidirectional manner, and an air passage closing position wherein the air from said surrounding atmosphere is prevented from reaching said vibrating chamber and said microphone operates in a polydirectional manner.

3. An adjustable condenser microphone adapted to operate in either a unidirectional or polydirectional manner, comprising, in combination, an open-ended casing; a diaphragm mounted at one end of said casing to hermetically seal the same from the surrounding atmosphere,

said diaphragm having an inner and outer surface and adapted to be vibrated by sound waves transmitted through said surrounding atmosphere and impinging on said diaphragm having an inner and outer surface and ed in said casing and spaced from said inner surface of said diaphragm; wall means forming a vibration chamber in said casing the volume of which is varied during vibration of said diaphragm; air passage means in said casing for providing a path for the flow of air between said vibration chamber and said surrounding atmosphere;

sage closing position wherein the air from said surrounding atmosphere is prevented from reaching said vibrating chamber and said microphone operates in a polydirectional manner; and means for normally urging said valve means into air passage closing position.

4 An adjustable condenser microphone adapted to operate in either a unidirectional or polydirectional manner, comprising, in combination, an open-ended casing; a diaphragm mounted at one end of said casing to hermetically seal the same from the surrounding atmosphere, said diaphragm having an inner and outer-surface and adapted to be vibrated by sound Waves transmitted through said surrounding atmosphere and impinging on said outer surface thereof; a rear electrode fixedly mounted in said casing and spaced from said inner surface of said diaphragm; wall means forming a vibration chamber in said casing the volume of which is varied during vibration of said diaphragm; air passage means in said casing for providing a path for the flow of air between said vibration chamber and said surrounding atmosphere; air delay means positioned in said casing in said path provided by said air passage means for introducing a predetermined delay in the flow :of air from said surrounding atmosphere to said vibration chamber; and valve means associated with said casing and movable between an air passage opening position, wherein the air from said atmosphere reaches said vibration chamber through said air passage means causing said microphone to operate in a unidirectional manner, and an air passage closing position wherein the air from said surrounding atmosphere is prevented from reaching said vibrating chamber and said microphone operates in a polydirectional manner.

5. An adjustable condenser microphone adapted to operate in either a unidirectional or polydirectional manner, comprising, in combination, an open-ended tubular casing; a diaphragm mounted at one end of said tubular casing to hermetically seal the same from the surrounding atmosphere, said diaphragm having an inner and outer surface and adapted to be vibrated by sound waves transmitted through said surrounding atmosphere and impinging on said outer surface thereof; a rear electrode fixedly mounted in said casing symmetrically about the axis thereof and having a planar face spaced from said inner surface of said diaphragm; wall means forming a vibration chamber in said casing the volume of which is varied during vibration of said diaphragm; air passage means in said casing for providing a path for the flow of air between said vibration chamber and said surrounding atmosphere; and valve means associated with said casing and movable between an air passage opening position, wherein the air from said atmosphere reaches said vibration chamber through said air passage means causing said microphone to operate in a unidirectional manner, and an air passage closing position wherein the air from said surrounding atmosphere is prevented from reaching said vibrating chamber and said microphone operates in a polydirectional manner.

6. An adjustable condenser microphone adapted to operate in either a unidirectional or polydirectional manner, comprising, in combination, an open-ended casing; a diaphragm mounted at one end of said casing to hermetically seal the same from the surrounding atmosphere, said diaphragm having an inner and outer surface and adapted to be vibrated by sound waves transmitted through said surrounding atmosphere and impinging on said outer surface thereof; a rear electrode fixedly mounted in said casing and spaced from said inner surface of said diaphragm; wall means forming a vibration chamber in said casing the volume of which is varied during vibra- 7 tion of said diaphragm; air passage means in said casing for providing a path for the flow of air between said vibration chamber and said surrounding atmosphere; and valve means associated with said casing and movable between an air passage opening position, wherein the air from said atmosphere reaches said vibration chamber through said air passage means causing said microphone to operate in a unidirectional manner, and an air passage "'8 closing position wherein the air from said surrounding atmosphere is prevented from reaching said vibrating chamber and said microphone operates in a polydirectional manner; and sound detour means mounted on said 5 casing adjacent said diaphragm.

No references cited. 

